Jerk, Acceleration and Junction Deviation in 3D Printing Explained

A printed cube with crisp corners and one with faint ghost lines beside every edge usually come off the same machine. The difference is jerk, acceleration and junction deviation in 3D printing, the three motion settings that decide how aggressively your printer changes direction. Get them wrong and you trade either speed for ringing artefacts or quality for slow, cautious moves. Get them right and the same hardware prints faster and cleaner.

Quick Answer

Acceleration controls how quickly the toolhead ramps from one speed to another, measured in mm/s squared. Jerk (in Marlin) or junction deviation (in Marlin 2.x and Klipper) sets how much instantaneous speed change is allowed at a corner without a full stop. Lower values mean cleaner corners but slower prints; a common safe starting point is 1500 to 2500 mm/s squared acceleration with junction deviation around 0.05.

What Each Setting Actually Does

Acceleration is the gentle one. When the printer needs to move from 0 to 150 mm/s, acceleration decides whether that ramp takes a long sweep or a sharp surge. High acceleration keeps the toolhead near its top speed for more of each line, which shortens print time, but it also throws more force into the frame and belts.

Jerk and junction deviation handle corners, where the maths gets interesting. At a 90 degree turn the toolhead has to reverse one axis while keeping another moving. A pure physics model would demand a full stop at every corner, which would make prints painfully slow. Jerk lets the printer "cheat" by permitting a small instantaneous velocity change instead of stopping. Junction deviation does the same job with a smarter model that accounts for the corner angle, so tight corners slow down more than gentle ones automatically.

How They Cause Ringing and Ghosting

Ringing, also called ghosting or echoing, shows up as repeating ripples just after a sharp feature, like a shadow of the corner printed into the wall. It happens when the toolhead changes direction fast enough to make the whole gantry vibrate, and the nozzle lays plastic while that vibration is still settling.

High acceleration and high jerk both feed this. The fix is to lower them until the ripples fade, then nudge back up to recover speed. If you own a printer with input shaping (common on newer boards), you can keep speeds high and let the firmware cancel the resonance instead, which is the better long term answer for anyone chasing both speed and finish.

Sensible Starting Values

For a typical bed-slinger printer, acceleration of 1500 to 2500 mm/s squared is a calm baseline. CoreXY machines with stiffer frames tolerate more. If your firmware uses classic jerk, 8 to 10 mm/s is conservative for the X and Y axes. If it uses junction deviation, start at 0.05 and raise it slowly; higher values round corners more aggressively and print faster.

Tune one variable per test print so you can actually see which change did what. A small calibration tower with sharp corners reveals ringing far faster than a finished model would. Stock up on filament and the right nozzles from the accessories range at Evetech before you start a long tuning session, since dialling these in burns through a few test cubes.

Frequently Asked Questions

Is jerk the same as junction deviation?

They solve the same problem, cornering speed, with different maths. Classic jerk allows a fixed instantaneous speed change regardless of corner angle, while junction deviation scales the allowed speed to how sharp the corner is. Junction deviation is generally the more refined of the two.

Will lowering acceleration always improve quality?

Up to a point. Lower acceleration reduces vibration and ringing, but past a certain value you only lose speed without seeing further gains. Find the threshold where artefacts disappear and stop there rather than crawling.

My corners look rounded, what is wrong?

Rounded corners usually mean junction deviation or jerk is set too high, so the toolhead carries too much speed through the turn. Drop the value and the corners sharpen up, at the cost of a slightly longer print.

Does a sturdier printer let me run higher values?

Yes. A rigid frame and tight belts resist the forces that high acceleration creates, so stiffer machines, especially CoreXY designs, hold quality at settings that would shake a lighter printer apart.